1. Field of the Invention
The present invention relates to a communication control technique in control stations.
2. Description of the Related Art
Wireless Universal Serial Bus (hereafter: WUSB) has been standardized as one of the communication methods in Wireless Personal Area Networks (WPAN).
WUSB is an extension of widely used USB standard to wireless domain, which has installed a plurality of products as wired communication standard. Aforementioned standard is publicly available as in URL=“http://www.usb.org/developers/wusb/”.
One of the characteristics of WUSB standard is partial simplification of wireless modulation method while compliant with WiMedia (one of the Ultra Wide Band communication method standard). Hereinafter, the wireless communication of aforementioned standard is explained using examples.
In wireless communication according to WUSB standard, each terminal is controlled to communicate with other terminals within the assigned time slot, based on time-division multiplexed system of fundamental WiMedia standard.
The communication slot assignment to each terminal is conducted by the terminal which acts as a control station (Host) by negotiate with the terminals which act as WiMedia-terminal according to the Wimedia standard. Moreover, at Host the allocated communication slot is segmented and by applied time-division multiplexing unique to WUSB standard, WUSB control data is transmitted to the Device. As mentioned above, Host of WUSB standard employs a hierarchized access control system.
In contrast, access control method of Device in WUSB standard is not always in compliant with WiMedia standard.
Stated differently, in case of Device in WUSB standard, while using WiMedia standard for wireless modulation methods, only a simplified WUSB standard is used as the access control method. By using such an approach, terminal architecture become simplified and power consumption of the terminal is reduced.
Access control method of Device compliant with simplified WUSB standard is explained below.
FIG. 10A is a representation of a wireless communication network (1005) constructed by wirelessly connecting Devices compliant with WUSB standard to Host compliant with WUSB standard. 1001 is a Host compliant with WUSB standard; 1003 and 1004 is Devices compliant with WUSB standard.
Moreover, FIG. 10B is a representation of, the time slot allocation based on Wimedia standard, and segmentation of the time slots based on time-division multiplexing unique to WUSB standard, with reference to FIG. 10A.
In WiMedia standard as discussed previously, Host (1001) starts time slot allocation as a terminal compliant with WiMedia standard (Hereinafter: WiMedia-terminal). In case of WiMedia time-division multiplexing, there is a time period where each WiMedia-terminal transmits each other control data (beacon) and a communication time slot (MAS) after aforementioned time period where each WiMedia-terminal communicates with others. By repeating these time periods as a supper-frame (broadcast-frame) at a constant frequency, time-shared controlling of multiplex communication between multiple WiMedia-terminal is implemented.
One cycle of Supper-frame contains 256 MAS, and each WiMedia-terminal secures its communication time slot sequentially based on this MAS unit. In WiMedia-terminals already connected to the network, the beacon transmitted by each terminal contains the occupied MAS information.
On the other hand, new WiMedia-terminal connecting the network analyzes the existing WiMedia-terminal beacons and selects a communication frame for itself without overlapping. In addition, negotiation protocol of the communication frame between WiMedia-terminals, is not directly related to present invention, and is not discussed.
In FIG. 10B-a, the state where Host (1001) has already ended the negotiation, and connected to the network as a WiMedia-terminal with an allocated time slot is represented. Beacon 1011˜1013 is sent at a constant frequency; and interval between two beacon starting points become 1 cycle of the Supper-Frame.
As shown in FIG. 10B-a, in one cycle of the Supper-Frame, the communication slot is separated into 3 MAS group 1014˜1016 and allocated to each WiMedia-terminals. Similarly, in next Supper-Frame, the communication slot is classified into 3 MAS group 1014˜1016 and allocated. However, because MAS positions are not constant, the MAS positions are updated due to WiMedia-terminal negotiations.
Here Host (1001) further segmentation of allocated MAS to create communication slots only compliant with WUSB.
More specifically, Host (1001) transmits irregular WUSB control information called Micro-scheduled Management Commands (MMC) to allocated MAS. Each MMC contains as indication information such as, Device identification information of communicable Devices compliant with WUSB standard in the slot following the MMC, information on communication slots position, and the next timing of MMC.
Instead, in each Device (Dev1(1003), Dev2(1004)) can obtain its allocated time slot by just analyzing MMC without considering beacon 1011˜1013 compliant with WiMedia standard. For this reason, in case each Device verifies the existence of its allocated time slot by MMC analyze, it conducts wireless communication with Host (1001) using this time slot.
As a result the Device receives the next MMC regardless of its' allocation or non-allocation of the time slot. It is necessary to obtain the next MMC transmitting timing to receive the next MMC.
As described above, in such access control method, the next MMC transmitting timing is obtained at the time MMC is received by the device compliant with simplified WUSB standard. Thus, even in case Hosts' (1001) MAS position information changed which obtained as a WiMedia-terminal, it can function as a device compliant with WUSB standard without any problems.
FIG. 10B-b represents the communication slot generation based on WUSB standard, in case Host (1001), Dev2 (1003) and Dev3 (1004) are connected into the wireless network 1005. As shown in FIG. 10B-b, inside MAS, MMC (1020˜1025), and communication slot of each device follow after aforementioned MMC is positioned sequentially.
In FIG. 10B-b to simplify the explanation consecutive MAC has only 1 MMC in each of them. However, in a Host compliant with WUSB standard, segmentation of MAS is possible due to various reasons such as, requests by connected various Devices compliant with WUSB standard, applications and etc. Then, for each time MMC is positioned. For that reason, in fact there might be plurality of MMC within each MAS.
However, in case wireless communication is conducted based on WUSB standard, a problem of unnecessary power consumption emerges when Device with low data rate requirements in relatively long periods is participated to the network. Concrete description is given using the FIG. 11A and FIG. 11B.
FIG. 11A shows a new condition of the network when Dev1 (1002) is participated to the network shown in FIG. 10A.
Dev1 (1002) depicted in FIG. 11A, is a device such as keyboard or mouse, which requires low data rate in relatively long periods. And, FIG. 11B depicts an example of communication slot construction.
As described above, in wireless communication according to WUSB standard, the communication slot that continues after MMC (1101˜1108) does not necessarily allocate communication slots for every device in the network. In case of communication slot (1107, 1108) of Dev1 (1002) is concerned, it is sufficient to allocate a narrow time slot with frequency of just once within the WiMedia-terminals' supper frame.
However, in each MMC contains the next MMC transmitting timing information. For this reason, Dev1 (1002) needed to receive and analyze MMC in order to preserve the wireless connection even in case it has no allocated communication slots.
Here, MMC is added depending on communication frame allocated as a WiMedia-terminal and number of devices connected to the same host. For this reason, for Devices such as Dev1 (1002) with relatively low frequency of communication, with MMC additions the time spend on MMC analyze unrelated to its communication become high, repetition of unnecessary data receiving operation is generated. Such receiving operation, increases the power consumption, especially in case of for Devices which use batteries, problem of battery life reduction is generated.